In addition to the unstable orbits, some BHs admit stable circular orbits for massive probes outside the photon-sphere that are known as ISCOs (Innermost Stable Circular Orbits) [1]}. The image produced by the ETH represents a combination of photon-sphere or photon-halo, in the case of rotating objects since \(r_c\)  depends on the value the angular momentum \(J\)  and \(J_z\)  of the probe, and emission from plasma populating the ISCOs, that depend on the angular momentum \(J\)  and \(J_z\)  of the probe, too [2]}, [3]}, [4]}, [5]}.
